Process for removal of radioactive contaminants



United States Patent 3,108,080 PROCESS FOR REMOVAL OF RADIOACTIVE CONTAMINANTS Elmer L. Brevik, Los Angeles, Calif., assignor, by mesne assignments, to Purex Corporation, Ltd., a corporation of California No Drawing. Filed Sept. 23, 1955, Ser. No. 536,297 3 Claims. (Cl. 252-137) This invention relates to the decontamination of surfaces on which are deposited radioactive materials, and is especially concerned with a novel composition and process for radioactive decontamination of the clothing of personnel handling radioactive materials.

In the manufacture and handling of radioactive materials, the equipment used in processing and the clothing of workers become contaminated with the radioactive materials to a degree where it becomes a health hazard to personnel. In the past, many such contaminated articles have been discarded because of uneconomical or impossible cleaning requirements. To alleviate this costly procedure, considerable research has been carried out on processes and compounds that will economically remove the radioactive contamination.

It has been known to employ a glassy phosphate in an effort to remove radioactive contamination from workmens clothing. It has also been known that sodium carbonate may be somewhat effective in the removal of radioactive contamination. These materials have been used either alone or in combinations with such cleaning aids as acetic acid and synthetic detergents. None of these materials, however, used either alone or in combination have proven entirely effective. In many instances, even repeated cleaning with the same reagent will not reduce the level of radioactivity below the point of safety.

One object of my invention is to provide a composition and process for the efficient removal of radioactive contamination from surfaces.

Another object is the provision of a composition and procedure for the radioactive decontamination of clothing, such as coveralls used by personnel handling radioactive materials.

A still further object is to afford a relatively inexpensive composition and economical process for removal of radioactive contamination from surfaces, and to elimi-' nate steps employed in conventional processes utilizing known compositions.

Other objects and advantages will be apparent from the following description of my invention.

I have found that a composition essentially comprising a glassy phosphate and either ammonium carbonate or ammonium bicarbonate, when used in a water solution, is highly effective in the removal of radioactive contaminants from surfaces, particularly clothing, and is much more effective in this respect than any of the prior art compositions.

Glassy phosphates have been defined in the literature as condensed phosphates having a Na O:P O ratio of from '0 to 1.7. The phosphate glass with a mol ratio of 1.0 has been called Grahams salt, and sometimes referred to as hexametaphosphate. The other glassy phosphates have been known as polyphosphates, the degree of polymerization being determined from their approximate analysis. See Properties of the Chemistry of Phosphorus, John R. Van Wazer, Interscience Encyclopedia, Inc., 1953.

The phosphates employed in my invention are polyphosphates which have a M O:P O ratio of about 0.9 to about 1.3, M being an alkali metal such as sodium, or ammonium. The term iglassy phosphate is employed 3,168,080 Patented Oct. 22, 1963 herein to denote and include any or all of these materials. Preferably, I employ glassy phosphates which when dissolved in water in a concentration of about 31 grams per liter of, solution give a pH of from about 6 to about 8. These include sodium polyphosphates such as sodium hexametaphosphate, and the equivalent alkali metal, e.g., potassium, polyphosphates and the equivalent ammonium polyphosphates. Also, the glassy phosphates of sodium in which the sodium cation is partially substituted with potassium or ammonium can be employed. The glassy phosphates defined above can be utilized individually or as mixtures of two or more of these materials.

The ammonium carbonate or ammonium bicarbonate is an essential ingredient of my composition. Mixtures of these ammonium salts can also be employed. These two ammonium compounds have proven about equally effective. There is believed to be a synergistic action between the ammonium ion, the carbonate or bicarbonate ion, and the above noted glassy phosphate or polyphosphate ion in solution, which give results far superior to, and highly unexpected from the prior art glassy phosphate or sodium carbonate compositions or other known compositions, in regard to effectiveness for removal of radioactive contamination, as will be shown hereinafter. An additional advantage is that the presence of the ammonium cation insures the completesolubility of the glassy phosphate, some forms of which are known to be relatively insoluble in water. The term carbonate containing material employed in the specification and claims is intended to denote a substance or compound having a carbonate or bicarbonate radical, and the term ammonium carbonate compound is intended to denote ammonium carbonate or ammonium bicarbonate.

The proportions of glassy phosphate and ammonium carbonate containing material which can be employed to obtain the improved results of the invention can be varied. However, tests have shown that a composition of about 50% glassy phosphate, e.g., sodium polyphosphate, and about 50% of the ammonium carbonate or bicarbonate is particularly effective. The invention composition when dissolved in water forms a solution having a pH of about 6 to about 9, usually about 7 to about 9. The concentration of the solid composition in the solution can be varied, a range of about 2 to about 8 ounces or more per gallon of solution being satisfactory, with a proportion of about 2.5 to about 5 ounces per gallon preferred.

I have found that the essential ions in my solutions for purposes of the invention are the ammonium cation, the

glassy phosphate or polyphosphate anion, and the carbonate or bicarbonate anion. Accordingly, it is understood that the source of the ammonium ion may be a compound other than ammonium carbonate or ammonium bicarbonate, e.g., ammonium hexametaphosphate or ammonium hydroxide, and the source of the carbonate or bicarbonate anion may be a compound such as sodium carbonate or sodium bicarbonate.

In addition to the aqueous solution of the invention preferably containing a glassy phosphate and an ammonium carbonate compound, small amounts, e.g., 4 or 5%, of synthetic detergents or wetting agents, improves the effectiveness of the solution in the decontamination of clothing, and also improves the detergency', rinsing and texture of the clothing in the laundering operation. However, it is to be understood that such detergent or wetting agent additives are not essential to the invention.

In normal commercial laundering operations, the fiber of the materials being laundered .is cleaned by strong 'alkalies followed by a subsequent acid sour, the purpose of the sour being to remove all alkalinity so that the clothing in contact with the skin will not cause irritation of the skin. The composition and process of my invention, in addition to their effectiveness for removal of radioactive contamination, have the added advantage for laundering purposes of not requiring a subsequent acid sour, since my composition at all concentrations in Water solution produces a pH suiiiciently close to neutra, as indicated above, to avoid this additional step. At this pH, the cleaning solution will produce no irritating effect on the skin even if the fiber is inadequately rinsed. This advantage materially reduces' the time of the operation and eliminates the need for the acid sour, resulting in additional economy of operation.

The tests on removability of radioactive contamination according to my invention were conducted on four types of radioactive sources, namely: uranium, plutonium, fission products (composition unknown) and soft beta radiation emitters. The plutonium and uranium were tested for removability of alpha radiation and the fission products and soft beta for removal of materials emitting the combination of beta-gamma rays. The materials emitting beta and gamma rays were included as one category because the counting devices determined the radiation level of both these products. The results of these tests showed removal in excess of 99% of all contaminants emitting alpha rays and 93% or more of contaminants emitting beta-gamma radiation. The tests were conducted on a large number of garments classified under three levels of contamination which were characterized as high level, medium level, and low level contamination.

The tests were conducted in a cascade-type washer constructed of monel metal or stainless steel. In no instance was a redeposition of the radioactive emitters noted, indicating eifectiveness of the invention composition and process for the removal of contamination from metal as well as clothing. The invention composition may also be effective in the removal of radioactivity from other types of surfaces such as concrete, rubber, canvas and wood. Temperatures of the laundering operation are those conventionally employed, e.g., from 160 F. to 180 F.

The following examples serve to illustrate the invention:

EXAMPLE I Composition A Percent Sodium polyphosphate (Na O:P O ratio of 1.2) 46 Ammonium bicarbonate 50 Wetting agent: Nacconol NR (a sodium alkyl aryl sulfonate detergent), or Triton X-100 (an alkylated aryl polyether alcohol non-ionic detergent) 4 The solution was tested on clothes contaminated with radioactive substances. The clothes were first rinsed with fresh water and then subjected to washing in the above solution of the invention containing sodium polyphosphate and ammonium bicarbonate for 15 minutes, with the solution at 175 F. The pH of the solution was about 7.5. No acid sours were necessary following washing because of the low alkalinity of the decontaminating solution of the invention.

The clothes were contaminated with four known contaminants, namely: radioactive products of uranium, fission products, radioactive products of plutonium, and material emitting soft beta rays. The composition of the fission products was not known but no alpha emitters were present in this contaminant. The composition of the materials emitting soft beta rays was also unknown.

The contaminants were tested at three levels, arbitrarily chosen by the degree of emission. The low level contamination for beta and gamma emitters started at 400 counts per minute; the highest level of contamination for beta and gamma emitters was 40,000 counts per min- Percent Removed Contaminant Alpha Beta-Gamma Radioactive products of Plutonium Radioactive products of Uranium Fission products Material emitting soft Beta radiat approx. 100

EXAMPLE 2 Tests similar to the tests of Example 1 were carried out using the same procedure and the same composition A of Example 1, except that ammonium carbonate was substituted for ammonium bicarbonate. The pH of the solution was 8.7. The results obtained were similar to those in Example 1.

EXAMPLE 3 Results similar to those of Example 1 are obtainable employing in composition A sodium hexametaphosphate (Na O:P O ratio of 1.0) in place of the sodium polyphosphate of Example 1.

EXAMPLE 4 Results similar to those of Example 1 are obtainable employing composition A in solution at a concentration of 4 ounces per gallon.

The results were further correlated by the determination of the number of garments that were rejected on a run that consisted of a number of loads of contaminated garments processed substantially according to Example 1. The safe contamination which must be met before a garment is considered safe for reuse is 360 counts per minute for beta-gamma radiation and 500 counts per minute for alpha radiation. The results based upon the number of garments processed versus the rejects is as follows:

BETA-GAMlVIA CONTAMINATION Comparative tests for removal of radioactive contaminants were run employing solutions according to the invention and prior art solutions, including those containing a glassy phosphate and sodium carbonate, but no ammonium ion. In all instances, the invention composition containing a glassy phosphate as above described and ammonium carbonate or bicarbonate, was superior in effectiveness to these conventional laundering compositions and processes known for this purpose.

The laundering operation according to the process of the invention, preferably employing my glassy phosphateammonium carbonate or bicarbonate composition, moreover has the advantage of being in the nature of a normal cleaning or laundering procedure with the important and economical exception that it is not necessary to use the conventional acid sour and numerous rinses after cleaning.

The invention composition is preferably almost neutral when dissolved in water and will therefore not produce chapping or skin irritation from retained alkalinity on the surfaces of the clothing, which is so noticeable with the highly alkaline compounds formerly used in laundering operations for radioactive decontamination purposes. Further, the solutions of the invention do not produce undesirable corosion of the metal surfaces of the laundering equipment, e.g., made of monel or stainless steel, with which such solutions come into contact.

While I have described a particular emodiment of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiations from a surface, which comprises contacting said surface with an aqueous solution comprising a mixture which consists essentially of a water soluble glassy phosphate in the form of a polyphosphate having a M O:P O mol ratio of about 0.9 to about 1.3, M being a member of the group consisting of alkali metal and ammonium, and a salt chosen from the group consisting of ammonium carbonate and ammonium bicarbonate, said mixture when dissolved in water forming a solution having a pH of from about 6 to about '9.

2. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface, which comprises contacting said surface with an aqueous solution comprising a mixture which consists essentially of a water soluble glassy phosphate of sodium having a Na O:P O mol ratio of about 0.9 to about 1.3, and a salt chosen from the group consisting of ammonium carbonate and ammonium bicarbonate, said mixture when dissolved in water forming a solution having a pH of from about 6 to about 9, the total concentration of said mixture being about 2 to about 8 ounces per gallon of solution.

3. A process effective for removal of radioactive contaminants emitting alpha, beta or gamma radiation from a surface, which comprises contacting said surface with an aqueous solution comprising a mixture which consists essentially of about equal proportions by weight of a water soluble glassy phosphate in the form of a sodium polyp hosphate having a Na O:P O mol ratio of about 0.9 to about 1.3, and a salt chosen from the group consisting of ammonium carbonate and ammonium bicarbonate, said mixture when dissolved in water forming a solution having a pH of about 7 to about 9, the total concentration of said mixture being about 2.5 to about 5 ounces per gallon of solution.

References Cited in the tile of this patent UNITED STATES PATENTS Re. 19,719 Hall Oct. 8, 1935 1,956,515 Hall Apr. 24, 1934 2,134,346 Slefert Oct. 25, 1938 2,215,814 Hall Sept. 24, 1940 2,445,893 Tjoflat July 27, 1948 2,731,420 Sylvester Jan. 17, 1956 2,924,576 Bersworth et al. Feb. 9, 1960 FOREIGN PATENTS 610,201 Great Britain Oct. 12, 1948 OTHER REFERENCES Snell, Foster 13., Inc., Removal of Radioactive Contaminants, in Soap and Sanitary Chemicals, October 1953, pp. 42-44.

Segura et al.: Detergency as Applied to Radiological Decontaminations, Chemistry and tllndustry, London, Nov. 28, ,1953, pp. 1270-1273.

A Study of the Efleetiveness of Decontaminating Agents in Contaminated Protective Clothing, by I. L. Norwood, July .29, 1955, printed by U.S. Atomic Energy Commission (HW-382l8 Rev.). 

1. A PROCESS EFFECTIVE FOR REMOVAL OF RADIOACTIVE CONTAMINANTS EMITTING ALPHA, BETA OR GAMMA RADIATIONS FROM A SURFACE, WHICH COMPRISES CONTACTING SAID SURFACE WITH AN AQUEOUS SOLUTION COMPRISING A MIXTURE WHICH CONSISTS ESSENTIALLY OF A WATER SOLUBLE GLASSY PHOSPHATE IN THE FORM OF A POLYPHOSPHATE HAVING A M2O:P2O5 MOL RATIO OF ABOUT 0.9 TO ABOUT 1.3, M BEING A MEMBER OF THE GROUP CONSISTING OF ALKALI METAL AND AMMONIUM, AND A SALT CHOSEN FROM THE GROUP CONSISTING OF AMMONIUM CARBONATE AND AMMONIUM BICARBONATE, SAID MIXTURE WHEN DISSOLVED IN WATER FORMING A SOLUTION HAVING A PH OF FROM ABOUT 6 TO ABOUT
 9. 